Actually, I have no idea. Good question.
My thoughts are that if the bees go out of their way to gather it, they probably know best.
Bees will gather all sorts of things are often seen on manure ples and other surprising places. It is thought that they find minerals and other things of interest to them there and mine the resource.
I doubt the flavour will show up in the honey, due to the small amount and the fact that there is little sugar in the grounds. Whatever they are doing with it, they are not making honey from it.
Is it nutritious and would they take it in larger amounts? Don't know. You might examine the pollen baskets of the bees and your combs to see how they transport it and if they are storing it like pollen.